Logorithms

A logarithm of a given number to a given base is the power to which you need to raise the base in order to get the number.

In general n = log(x) (given the log's base equals b) because x = b^n
and for natural logs, n=ln(x) because x = e^n (the l in ln is lowercase L)
We generally assume that if the base isn't specified, the base is 10 (log(100) = 2 because 10^2 = 100)